The present invention relates to a throttle control apparatus for controlling the amount of intake air in an internal combustion engine. More particularly, the present invention relates to an improvement in reliability of a throttle sensor for detecting the degree of opening of a throttle valve.
There have heretofore been motor-driven throttle control apparatus adapted to control the engine speed by opening or closing a throttle valve secured to a throttle shaft with a motor rotating according to a signal from an ECU (Electronic Control Unit) through gears (a reduction gear mechanism). A publicly known throttle control apparatus of this type has a driving gear secured to an output shaft of a motor, a throttle gear secured to a throttle shaft, an intermediate gear intervening between the two gears, a return spring for urging a throttle valve in the direction in which it is closed, a throttle sensor unit (hereinafter referred to as simply xe2x80x9csensor unitxe2x80x9d) for detecting the degree of opening of the throttle valve, etc. Both ends of the throttle shaft project outward from bearings provided in a throttle body member. A reduction gear mechanism is connected to one end of the throttle shaft. The sensor unit is connected to the other end of the throttle shaft (for example, see Japanese Patent Application Unexamined Publication (KOKAI) No. Hei10-159591).
In the prior art disclosed in the above-mentioned JP(A) Hei10-159591, the reduction gear mechanism is connected to one end of the throttle shaft, and the sensor unit is connected to the other end of the throttle shaft. Therefore, it is necessary to provide a gear case at one end of the throttle shaft and to provide a sensor case at the other end of the throttle shaft. This causes the throttle body to become complicated in structure and the number of components to increase unfavorably. Under these circumstances, an invention was made to improve the prior art disclosed in JP(A) Hei10-159591. With the invention, the reduction gear mechanism, the sensor unit, etc. are disposed at one end of the throttle shaft and accommodated in a single chamber (see Japanese Patent Application Unexamined Publication (Kokai) No. 2000-265861, by the present applicant). In this invention, as shown in FIGS. 2 and 11, a driving gear 20, an intermediate gear 22, a throttle gear 18, a full-closed position adjusting screw 23, a brush 16 for a throttle sensor, a sensor substrate 17, etc. are surrounded by a cover 32 and accommodated in the same chamber.
If the reduction gear mechanism, the sensor unit, etc. are accommodated in a single chamber, sliding wear particles produced between gears or those produced between a spring and a guide contacting it are likely to enter and accumulate in the area between the brush and the substrate (resistor) in the sensor unit, causing a contact failure and making it impossible to detect an accurate throttle opening. One approach to solve this problem is to install the sensor unit, which includes the brush and the substrate, in the vicinity of a throttle bore portion of the throttle shaft and to cover the sensor unit with a lidded cylindrical cover arranged to fit to the throttle body member, thereby preventing sliding wear particles produced between the components from entering the sensor unit. In this case, however, vibration friction particles produced by engine vibrations occurring between the cover and the throttle body member may accumulate in the area between the brush and the substrate, causing a contact failure and making the sensor unit unable to detect an accurate throttle opening. In addition, because the sensor unit is provided in an inner part near the throttle bore, it is difficult to perform an operation for measuring the brush pressing force during the assembly of the throttle body. Therefore, the number of man-hours needed to carry out the operation increases, causing the assembling cost to be increased.
A first object of the present invention is to provide a throttle control apparatus for an internal combustion engine in which wear particles due to sliding between components and vibration wear particles produced between components by engine vibrations are prevented from entering the area between a brush of a throttle sensor and a sensor substrate (resistor) to prevent the occurrence of a contact failure between the brush and the substrate, thereby making it possible to detect an accurate throttle opening. A second object of the present invention is to reduce the number of man-hours needed to carry out the assembling operation and to thereby reduce the assembling cost.
A third object of the present invention is to provide a throttle control apparatus for an internal combustion engine in which a sensor chamber is formed outside a cover for a gear chamber to accommodate a sensor unit, and a breather opening is provided in the wall of the sensor chamber. The throttle control apparatus is designed to prevent wear particles in the gear chamber, when entering the sensor chamber through the breather opening, from adhering to the sensor unit in the sensor chamber. A fourth object of the present invention is to prevent the breather opening from being clogged with drops of water entering the sensor chamber or the gear chamber.
The present invention is applied to a throttle control apparatus for an internal combustion engine in which a throttle shaft rotatably provided across an intake passage is rotatively driven by a motor through gears (reduction gear mechanism) to open or close a throttle valve secured to the throttle shaft, thereby controlling the amount of intake air. According to a first aspect of the present invention, a brush of a sensor unit for detecting a degree of opening of the throttle valve is secured to an outer end portion of the throttle shaft projecting from a cover, and the sensor unit is accommodated in a sensor chamber formed outside the cover and isolated by a seal member from a gear chamber for accommodating the gears. With the arrangement according to the first aspect of the present invention, a sensor chamber is constructed of a cover and a plate separately from the gear chamber, and the sensor unit is accommodated in the sensor chamber. Therefore, wear particles due to sliding and vibrations occurring in the gear chamber will not enter the sensor chamber and accumulate in the area between the brush and the sensor substrate to cause a contact failure. Accordingly, the throttle opening detecting capability will not degrade, and it is possible to detect an accurate throttle opening.
According to a second aspect of the present invention, the brush of the sensor unit in the first arrangement is secured to the outer side of a brush lever to extend outward. With the arrangement according to the second aspect of the present invention, because the brush is secured to the outer side of the brush lever to extend outward, it becomes easy to measure the brush pressing force during the assembly of the throttle body. Accordingly, it is possible to reduce the number of man-hours needed to perform the assembling operation and hence possible to reduce the assembling cost.
According to a third aspect of the present invention, a breather opening is provided in the wall of the sensor chamber for accommodating the sensor unit in the first and second arrangements. With the arrangement according to the third aspect of the present invention, because a breather opening is provided in the wall of the sensor chamber for accommodating the sensor unit, it is possible to prevent the brush and the sensor substrate from being corroded by a corrosive gas generated from a synthetic resin or rubber material used in the sensor chamber by scavenging the corrosive gas through the breather opening.
According to a fourth aspect of the present invention, a fixed shaft for an intermediate gear is supported at both ends thereof by a throttle body member and the cover in the first to third arrangements. With the arrangement according to the fourth aspect of the present invention, because both ends of the fixed shaft for the intermediate gear are supported, driving force from a driving gear is halved by bearing portions for the two ends of the shaft. Accordingly, the length to which the fixed shaft is press-fitted into the throttle body member can be reduced to half. In addition, the amount of distortion of the fixed shaft reduces by half, and the amount of sliding between the gears also reduces. Consequently, the amount of wear particles due to sliding reduces, and the durability of the gears is improved.
According to a fifth aspect of the present invention, a breather opening is provided at a position facing a position laterally away from a resistor buried in the sensor substrate in the first arrangement. With the arrangement according to the fifth aspect of the present invention, because the breather opening is provided at a position facing a position laterally away from the resistor buried in the sensor substrate, when wear particles in the gear chamber enter the sensor chamber through the breather opening, the wear particles are unlikely to adhere to the resistor. Thus, the effect of wear particles on the sensor output signal is reduced.
According to a sixth aspect of the present invention, the breather opening is provided at a position facing a position away from a brush position when the throttle valve is fully open, which is less frequently used than a brush position when the throttle valve is fully closed, to the outside of the movable range of the brush in the third or fifth arrangement. With the arrangement according to the sixth aspect of the present invention, the breather opening is provided at a position facing a position away from a brush position when the throttle valve is fully open, which is less frequently used than a brush position when the throttle valve is fully closed, to the outside of the movable range of the brush. Accordingly, when wear particles in the gear chamber enter the sensor chamber through the breather opening, the wear particles will adhere to a non-used portion of the resistor (a portion which the brush will not contact) or to a portion of the resistor that is least frequently used. Therefore, the effect of wear particles on the sensor output signal is reduced. In addition, because wear particles will adhere to the non-used portion of the resistor or the least frequently used portion thereof, it is possible to prevent wear particles from being scattered over the whole area of the sensor substrate, including the resistor, by the brush.
According to a seventh aspect of the present invention, an auxiliary hole larger in diameter than the breather opening is formed at either or each of the sensor chamber side of the breather opening and the gear chamber side of the breather opening in the third arrangement in such a manner that a step portion is interposed between the breather opening and the auxiliary hole. With the arrangement according to the seventh aspect of the present invention, an auxiliary hole larger in diameter than the breather opening is formed at either or each of the sensor chamber side of the breather opening and the gear chamber side of the breather opening with a step portion interposed therebetween. Therefore, when drops of water entering the gear chamber or the sensor chamber move along the sensor chamber wall, the water drops are trapped in the auxiliary hole and the step portion and prevented from reaching the breather opening. Thus, the breather opening is prevented from being clogged with water. Accordingly, the discharge of a corrosive gas from the sensor chamber will not be obstructed.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.